Evaluation of captive bolus applicators

Three square (L, M, MS) and one rectangular (HN) applicators with captive boluses were provided by the Clini-Therm Corporation for evaluation. Surface cooling is achieved by attaching a mineral oil captive bolus to the built in water-circulating tubes at the aperture of the applicators. These applicators were tested on a phantom with a 2-cm fat slab over 10-cm-thick muscle. Surface and sagittal heating patterns were obtained using a thermograph. All captive-bolus applicators have heating patterns similar to that of the regular Clini-Therm applicators. Due to hot spots at the edges of the applicators where the E fields terminate, these modified applicators should not be placed in direct contact with patients when boluses are not used. Tests with Clini-Therm regular water bolus instead of the captive oil bolus indicated that the orientation of water flow should be parallel to the E field to minimize perturbation of the heating patterns. Thermal conduction studies showed that the captive bolus reacts too slowly for skin temperature control. The modified captive bolus applicators did not improve the performance of the system.     

Thermographically determined specific absorption rate patterns of 434-MHz applicators

The specific absorption rate (SAR) patterns of two 434-MHz hyperthermia applicators, models TCA 434-1 (9 X 20 cm) and TCA 434-2 (13 X 25 cm), were evaluated thermographically using a phantom model. The phantom model consisted of a 2-cm-thick layer of fat and a 10-cm depth of muscle contained in a 30 X 30 cm base Plexiglas box. The model was bisected in the middle. Polyester screens at the interface allowed the synthetic gel to make electrical contact between the two halves of the muscle tissue. Octyl alcohol was applied to the fat interface to ensure continuity of dielectric properties. Thermograms were taken for both applicators over the following areas of the exposed model: (1) fat surface, (2) internal surface with E-field parallel to interface, and (3) internal surface with E-field perpendicular to interface. SAR's were calculated from the temperature rise (8 degrees C maximum), net input power (550-650 W), exposure time (15-60 s), and specific heat of the muscle (0.86 kcal/kg degrees C). A factor of 0.42 needs to be multiplied to correct for the specific heat of fat. High localized SAR's along the broad sides of the applicators were seen when the applicators were in direct contact with the phantom. With the use of a 0.8-cm polystyrene foam spacing, the SAR's within the aperture of the applicators were relatively uniform. The patterns of the two applicators were quite similar. However, the TCA 434-1 applicator is smaller and more applicable for clinical conditions.     

Evaluation of multielement catheter-cooled interstitial ultrasound applicators for high-temperature thermal therapy

Catheter-cooled (CC) interstitial ultrasound applicators were evaluated for their use in high-temperature coagulative thermal therapy of tissue. Studies in ex vivo beef muscle were conducted to determine the influences of applied electrical power levels (5-20 W per element), catheter flow rate (20-60 ml min(-1)), circulating water temperature (7-40 degrees C), and frequency (7-9 MHz) on temperature distribution and thermal lesion geometry. The feasibility of using multiple interstitial applicators to thermally coagulate a predetermined volume of tissue was also investigated. Results of these studies revealed that the directional shape of the thermal lesions is maintained with increasing time and power. Radial depths of the thermal lesions ranged from 10.7 +/- 0.7 mm after heating for 4 min with an applied power level of 5 W, to 16.2 +/- 1.4 mm with 20 W. The axial length of the thermal lesions is controlled tightly by the number of active transducers. A catheter flow rate of 20 to 40 ml min(-1) (52.2 +/- 5.5 kPa at 40 ml min(-1)) with 22 degrees C water was determined to provide sufficient cooling of the transducers for power levels used in this study. In vivo temperatures measured in the center of a 3-cm-diam peripheral implant of four applicators in pig thigh muscle reached 89.3 degrees C after 4 min of heating, with boundaries of coagulation clearly defined by applicator position and directivity. Conformability of heating in a clinically relevant model was demonstrated by inserting two directional CC applicators with a 2 cm separation within an in vivo canine prostate, and generating a thermal lesion measuring 3.8 cm x 2.2 cm in cross section while directing energy away from, and protecting the rectum. Maximum measured temperatures at midgland exceeded 90 degrees C within 20 min of heating. The results of this study demonstrate the utility of single or multiple CC applicators for conformal thermal coagulation and high temperature thermal therapy, with potential for clinical applications in sites such as prostate, liver, breast, or uterus.     

Specific absorption rates in simulated tissue media for a 10 x 10 cm 915-MHz waveguide applicator

The use of hyperthermia in combination with radiotherapy is currently being investigated at many cancer treatment facilities. Several different types of heating modalities are presently being used and for each of these systems it is important to determine the power distributions of their hyperthermia applicators in tissue-equivalent phantoms. This information will be used for treatment planning, routine quality assurance, and acceptance testing as well as for comparison between these various modalities and systems. This report describes the power distribution characteristics of the Clini-Therm 10 x 10 cm 915-MHz waveguide applicator measured within muscle tissue phantom materials arranged in several clinically relevant treatment configurations. The net increase in temperature that resulted from 20-s pulses of microwave power was measured at various points within each phantom by the system's implantable fiberoptic temperature sensors. From these temperature measurements the distribution of power was calculated as specific absorption rates (SAR). The results are displayed as two-dimensional ISO-SAR maps which relate power levels throughout the irradiated volume to those obtained on the central axis of the applicator. When the applicator was in direct contact with the muscle phantom the highest SAR measured was 2 cm lateral to its central axis along the muscle surface. On the central axis approximately 50% of the power was attenuated by each centimeter of muscle material. The introduction of either fat, bone, or a water-filled pad between the applicator and the muscle altered the pattern of power distribution within the irradiated volume without substantially altering the relative distribution of power along the central axis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Control of interstitial thermal coagulation: comparative evaluation of microwave and ultrasound applicators

This study presents a comparative evaluation of the control of heating and thermal coagulation with microwave (MW) and ultrasound (US) interstitial applicators. Helical coil MW antennas (17 mm and 25 mm length radiating antennae) were tested using an external implant catheter (2.2 mm o.d.) with water-cooling. US applicators with tubular transducers (2.2 and 2.5 mm o.d., 10 mm length, single-element and 3-element) were utilized with a direct-coupled configuration and internal water-cooling. Measurements of E-field distributions (for MW) and acoustic beam distributions (for US) were used to characterize the applicator energy output. Thermal performance was evaluated through multiple heating trials in vitro (bovine liver) and in vivo (porcine thigh muscle and liver) at varied levels of applied power (20-40 W for microwave, 15-35 W for ultrasound) and heating times (0.5-5 min). Axial temperature distributions in the tissue were recorded during heating, and dimensions of the resulting lesions of thermal coagulation were measured. Both MW and US applicators produced large volumes of tissue coagulation ranging from 8 to 20 cm3 with singular heating times of 5 min. Radial depth of lesions for both MW and US applicators increased with heating duration and power levels, though US produced notably larger lesion diameters (30-42 mm for US vs 18-26 mm for MW, 5 min heating). Characteristic differences between the applicators were observed in axial energy distribution, tissue temperatures, and thermal lesion shapes. MW lesions increased significantly in axial dimensions (beyond the active applicator length) as applied power level and/or heating duration was increased, and lesion shapes were generally not uniform. US provided greater control and uniformity of heating, with energy deposition and axial extent of thermal lesions corresponding to the length of the active transducer(s). The improved ability to control the extent of thermal coagulation demonstrated by the US applicators provides greater potential to target a specific region of tissue.     

Theoretical model of internally cooled interstitial ultrasound applicators for thermal therapy

Interstitial ultrasound applicators for high-temperature thermal therapy are currently being developed for treating cancerous and benign disease. Internally cooled, direct-coupled (ICDC) applicators, composed of a segmented array of cylindrical ultrasound transducers, have demonstrated capabilities of producing controllable and conformal heating distributions along the applicator length and angular orientation. In this study, 2D transient acoustic and biothermal models of ICDC applicators were developed using a mixed implicit and explicit finite difference solution with variable node spacing in cylindrical coordinates for enhanced speed, stability and accuracy. The model incorporates dynamic behaviour of acoustic parameters and blood perfusion as a function of temperature and thermal dose. Acoustic intensity distributions were modelled as a composite of measured and theoretical intensity distributions. The shape and time evolution of temperature contours and thermal lesions for 90 degrees, 200 and 360 degrees angularly directional applicators and multi-transducer applicators were modelled for heating durations between 1 and 5 min. Model parameters were selected to match previously reported ex vivo and in vivo studies of 2.2 mm diameter ICDC devices in thigh muscle and liver (15-30 W cm(-2) applied power density, 0.5-5 min treatment times, 2.8-3.6 cm diameter thermal lesions). The temperatures and lethal thermal dose (600 EM43 degrees C) contours calculated using the models were in excellent agreement with temperatures and thermal lesion dimensions (visible coagulation) determined experimentally. The differences between maximum radial depths of coagulation calculated using the r-z and r-theta models were small, less than approximately 2 mm for 10-15 mm lesions. There was a strong correlation between the calculated 50 degrees C contour and the radial, angular and axial lesion dimensions obtained for 3-5 min heating protocols. The models developed in this study have significant application in design studies and potential future use in treatment planning of ICDC interstitial ultrasound thermal therapy.     

Comparison of muscle cross-sectional area and strength between untrained women and men

The cross-sectional areas (CSA) of fat, muscle and bone tissues of the limb as well as maximal voluntary isokinetic strength were measured in untrained men (n=27) and women (n=26) aged 18–25 years. Anatomical CSA of the three tissues were determined by ultrasound on the upper arm and thigh. The isokinetic strength of the elbow and knee extensor and flexor muscles were measured by an isokinetic dynamometer (Cybex 11) at 1.05 rad · s^–1. The women had significantly (P<0.001) larger fat CSA and smaller bone and muscle CSA than the men in both the upper arm and thigh. Among tissue CSA, the largest difference between the women and men was found in fat CSA regardless of the measurement sites. The sex differences in bone and muscle CSA were found largely in the upper arm compared to the thigh, even when expressed per unit second power of the limb length. Regression analyses of the data for respective samples for the men and women showed significant correlations (r=0.411–0.707, P < 0.05–P < 0.001) between CSA and strength in all muscle groups except for the elbow extensors of the men (r=0.328, P>0.05) and the elbow flexors of the women (r=0.388, P>0.05). No significant difference between sexes was observed when strength was expressed per unit of muscle CSA (F · CSA^–1) for the elbow flexors and extensors. However, the men showed significantly higher F · CSA^–1 than the women for the knee flexors and extensors (P < 0.001). These results would indicate that, although the difference between sexes in muscle CSA is smaller in the thigh than in the upper arm, differences in the ability to develop dynamic strength proportional to the CSA appeared mainly in the thigh muscles compared to the upper muscles.     

Performance characteristics of a helical microwave interstitial antenna for local hyperthermia

A helical microwave antenna has been designed to improve heat deposition by interstitial applicators used for clinical hyperthermia. Iso-specific-absorption-rate (SAR) curves of the helical antenna as well as a conventional monopole antenna were measured and compared in both muscle and brain tissue phantoms. The heating pattern of the helical antenna is more uniform along the length of the antenna which has important implications for multiarray implant configurations.     

MOSFET dosimeter depth-dose measurements in heterogeneous tissue-equivalent phantoms at diagnostic x-ray energies

The objective of the present study was to explore the use of the TN-1002RD metal-oxide-semiconductor field effect transistor (MOSFET) dosimeter for measuring tissue depth dose at diagnostic photon energies in both homogeneous and heterogeneous tissue-equivalent materials. Three cylindrical phantoms were constructed and utilized as a prelude to more complex measurements within tomographic physical phantoms of pediatric patients. Each cylindrical phantom was constructed as a stack of seven 5-cm-diameter and 1-cm-thick discs of materials radiographically representative of either soft tissue (S), bone (B), or lung tissue (L) at diagnostic photon energies. In addition to a homogeneous phantom of soft tissue (SSSSSSS), two heterogeneous phantoms were constructed: SSBBSSS and SBLLBSS. MOSFET dosimeters were then positioned at the interface of each disc, and the phantoms were then irradiated at 66 kVp and 200 mAs. Measured values of absorbed dose at depth were then compared to predicated values of point tissue dose as determined via Monte Carlo radiation transport modeling. At depths exceeding 2 cm, experimental results matched the computed values of dose with high accuracy regardless of the dosimeter orientation (epoxy bubble facing toward or away from the x-ray beam). Discrepancies were noted, however, between measured and calculated point doses near the surface of the phantom (surface to 2 cm depth) when the dosimeters were oriented with the epoxy bubble facing the x-ray beam. These discrepancies were largely eliminated when the dosimeters were placed with the flat side facing the x-ray beam. It is therefore recommended that the MOSFET dosimeters be oriented with their flat sides facing the beam when they are used at shallow depths or on the surface of either phantoms or patients.     

The influence of skeletal muscle anisotropy on electroporation: in vivo study and numerical modeling

The aim of this study was to theoretically and experimentally investigate electroporation of mouse tibialis cranialis and to determine the reversible electroporation threshold values needed for parallel and perpendicular orientation of the applied electric field with respect to the muscle fibers. Our study was based on local electric field calculated with three-dimensional realistic numerical models, that we built, and in vivo visualization of electroporated muscle tissue. We established that electroporation of muscle cells in tissue depends on the orientation of the applied electric field; the local electric field threshold values were determined (pulse parameters: 8 × 100 μs, 1 Hz) to be 80 V/cm and 200 V/cm for parallel and perpendicular orientation, respectively. Our results could be useful electric field parameters in the control of skeletal muscle electroporation, which can be used in treatment planning of electroporation based therapies such as gene therapy, genetic vaccination, and electrochemotherapy.     

Thigh composition in young and elderly men determined by computed tomography.

Computed tomography (CT) was used to quantify components of the thigh in young (n = 13) and elderly (n = 11) men. Cross-sectional areas (CSA) of the total limb, total muscle plus bone, quadriceps compartment, hamstring compartment and bone were measured at each of five scan sites along the length of the thigh. Non-muscle tissue (NMT) areas within the muscle compartments were measured using changes in density based on Hounsfield units. Skin plus subcutaneous fat areas and quadriceps and hamstring lean muscle areas were calculated by subtraction. Geometric formulae were used to calculate related volumes for each thigh component. Volumes were also predicted from regression equations employing thigh length and component CSA from single mid-limb CT scans. The results showed that while total thigh CSA was not different in elderly men, they had significantly smaller total muscle plus bone (13.0%), and quadriceps (26.4%), and hamstring (17.9%) muscle areas. The elderly men also had significantly greater CSA for skin plus subcutaneous fat (37.6%), and for NMT in the quadriceps (59.4%) and hamstring (127.3%) muscle compartments. These results suggest that comparisons of relative leg muscle strength between young and elderly men may be misleading due to the decrease in actual muscle tissue associated with ageing. Appropriate quantification of muscle size and CSA must be carried out before such comparisons can be meaningful.     

Human leg heating using a mini-annular phased array

The energy deposition pattern within an isolated human leg heated with a mini-annular phased array (MAPA) hyperthermia applicator has been determined. The non-tumor-bearing lower portion of a human leg amputated at the hip due to the presence of a large tumor in the thigh was "fixed" in a 50% ethanol in 0.9% saline solution. Subsequent to this fixation process, the leg was rehydrated in 0.9% saline and heated four times using a MAPA operating at 122 MHz. Specific absorption rates and electric field strengths were calculated from the rates of change of temperature with time measured at 143 different anatomical locations within the leg. When the leg was coaxial with the MAPA and the MAPA was axially positioned midway between the knee and the ankle, the points of maximum heating were skewed away from the center of the MAPA, towards the ankle of the leg and along the central axis of the MAPA. Significant temperature rise was measured inside the bone and the fat as well as inside the muscle of the leg. Bone heating was reduced when the leg was shifted away from the MAPA axis.     

Multisectored interstitial ultrasound applicators for dynamic angular control of thermal therapy

Dynamic angular control of thermal ablation and hyperthermia therapy with current interstitial heating technology is limited in capability, and often relies upon nonadjustable angular power deposition patterns and/or mechanical manipulation of the heating device. The objective of this study was to investigate the potential of multisectored tubular interstitial ultrasound devices to provide control of the angular heating distribution without device manipulation. Multisectored tubular transducers with independent sector power control were incorporated into modified versions of internally cooled (1.9 mm OD) and catheter-cooled (2.4 mm OD) interstitial ultrasound applicators in this work. The heating capabilities of these multisectored devices were evaluated by measurements of acoustic output properties, measurements of thermal lesions produced in ex vivo tissue samples, biothermal simulations of thermal ablation and hyperthermia treatments, and MR temperature imaging of ex vivo and in vivo experiments. Acoustic beam measurements of each applicator type displayed a 35 degrees -40 degrees acoustic dead zone between each independent sector, with negligible mechanical or electrical coupling. Thermal lesions produced in ex vivo liver tissue with one, two, or three sectors activated ranged from 13-18 mm in radius with contiguous zones of coagulation between active sectors. The simulations demonstrated the degree of angular control possible by using variable power levels applied to each sector, variable duration of applied constant power to individual sectors, respectively, or a multipoint temperature controller to vary the power applied to each sector. Despite the acoustic dead zone between sectors, the simulations also showed that the variance from the maximum lesion radius with three elements activated is within 4%-13% for tissue perfusions from 1-10 kg m(-3) s(-1). Simulations of hyperthermia with maximum tissue temperatures of 45 degrees C and 48 degrees C displayed radial penetration up to 2 cm of the 40 degrees C steady-state contour. Thermal characterizations of trisectored applicators in ex vivo and in vivo muscle, using real-time MR thermal imaging, reinforced angular controllability and negligible radial variance of the heating pattern from the applicators, demonstrated effective heating penetration, and displayed MR compatibility. The multisectored interstitial ultrasound applicators developed in this study demonstrated a significant degree of dynamic angular control of a heating pattern without device manipulation, while maintaining heat penetration consistent with previously reported results from other interstitial ultrasound applicators.     

大鼠腓肠肌细胞介电谱测量和Cole-Cole数学模型分析

测量大鼠腓肠肌细胞介电谱,利用Cole-Cole方程的曲线拟合建立Cole-Cole数学模型参数.在100 Hz～100 MHz频率范围,使用Agilent 4294A阻抗分析仪对电场与肌纤维方向呈平行和垂直的大鼠腓肠肌进行了阻抗测量,并利用Cole-Cole方程的数值计算,对细胞介电谱、Cole-Cole图、介电损耗因子频谱、电导率虚部频谱和损耗角正切频谱进行曲线拟合分析和残差分析,比较电场与肌纤维方向呈平行或垂直两种情况的介电行为区别.结果表明:骨骼肌细胞的介电弛豫具有两个特征频率,其平行方向的特征频率低于垂直方向;平行方向的介电增量高于垂直方向的介电增量;平行方向的低频极限量高于垂直方向的低频极限量;平行方向和垂直方向的介电常数高频极限量相等;平行方向和垂直方向的电导率高频极限量存在一定差距.平行方向的电导率虚部频谱和损耗角正切分别高于垂直方向的值,但是,平行方向的电导率虚部最大值低于其垂直方向的值.腓肠肌细胞的介电常数和电导率存在频率依存性和各向异性,其介电行为存在α和β两个介电散射,并满足Cole-Cole数学模型.     

Assessment of thermal coagulation in ex-vivo tissues using Raman spectroscopy

Raman spectroscopy is used to study the effects of heating on specific molecular bonds present in albumen-based coagulation phantoms and ex-vivo tissues. Thermal coagulation is induced by submerging albumen-based phantoms in a 75°C water bath to achieve target temperatures of 45, 55, 65, and 75°C. Laser photocoagulation is performed on ex-vivo bovine muscle samples, yielding induced temperatures between 46 and 90°C, as reported by implanted microthermocouples. All phantoms and tissue samples are cooled to room temperature, and Raman spectra are acquired at the microthermocouple locations. Shifts in major Raman bands are observed with laser heating in bovine muscle, specifically from the amide-1 α-helix group (～1655 cm(-1)), the CH(2)/CH(3) group (～1446 cm(-1)), the Cα-H stretch group (～1312 cm(-1)), and the CN stretch group (～1121cm(-1)). Raman bands at 1334 cm(-1) (tryptophan), 1317 cm(-1) [ν(Cα-H)], and 1655 cm(-1) (amide-1 α-helix) also show a decrease in intensity following heating. The results suggest that Raman band locations and relative intensities are affected by thermal denaturation of proteins, and hence, may be a useful tool for monitoring the onset and progression of coagulation during thermal therapies.     

The effect of coupling materials on specific absorption rate distributions at 915 MHz

Deionized water is commonly used to couple microwave applicators to the patient surface in the administration of local hyperthermia. Profiles of the specific absorption rate (SAR) at 1-cm depth show that deionized water coupling significantly distorts the SAR distributions of the Clini-Therm 915-MHz 10 X 10 and 15 X 15 cm2 applicators. Maxima and minima that are discernible in the SAR profiles obtained by direct applicator load contact are amplified producing unexpected hot and cold regions in the heating pattern. An exception is coupling achieved by use of the Clini-Therm cooling pad, oriented such that the direction of deionized water flow is perpendicular to the electric field. The distortion in the SAR distribution can also be eliminated by replacing deionized water with mineral oil, a material having a much lower dielectric constant (epsilon = 2). The SAR profiles for mineral oil coupling are comparable to those obtained for direct contact; however, the efficiency of power transfer is slightly less (70%) and the level of microwave leakage is approximately four times greater.     

Resistivity and phase in localized BIA.

We describe a system for highly reproducible non-invasive rf impedance measurements as a function of position along body segments such as the thigh. Results are reported for mainly healthy male and female subjects ranging in age from 19 to 65 and in body-mass index from 15 to 40. A principal conclusion is that the phase of the impedance falls monotonically with increasing distance from the knee, with average values substantially above what is found using standard, whole-body bioelectrical impedance analysis (BIA). To compensate for thigh shape, the data are further analysed using an anatomical model based on reasonable approximations for the distributions of muscle, fat and bone, yielding values of the effective resistivity for current flow parallel to the muscle fibres. The phase and resistivity results are discussed with reference to the whole-body BIA study of maintenance haemodialysis patients by Chertow et al, and in regard to possible physiological correlations observed in this work.     

A heterogeneous human tissue mimicking phantom for RF heating and MRI thermal monitoring verification

This paper describes a heterogeneous phantom that mimics a human thigh with a deep-seated tumor, for the purpose of studying the performance of radiofrequency (RF) heating equipment and non-invasive temperature monitoring with magnetic resonance imaging (MRI). The heterogeneous cylindrical phantom was constructed with an outer fat layer surrounding an inner core of phantom material mimicking muscle, tumor and marrow-filled bone. The component materials were formulated to have dielectric and thermal properties similar to human tissues. The dielectric properties of the tissue mimicking phantom materials were measured with a microwave vector network analyzer and impedance probe over the frequency range of 80-500 MHz and at temperatures of 24, 37 and 45 °C. The specific heat values of the component materials were measured using a differential scanning calorimeter over the temperature range of 15-55 °C. The thermal conductivity value was obtained from fitting the curves obtained from one-dimensional heat transfer measurement. The phantom was used to verify the operation of a cylindrical four-antenna annular phased array extremity applicator (140 MHz) by examining the proton resonance frequency shift (PRFS) thermal imaging patterns for various magnitude/phase settings (including settings to focus heating in tumors). For muscle and tumor materials, MRI was also used to measure T1/T2* values (1.5 T) and to obtain the slope of the PRFS phase change versus temperature change curve. The dielectric and thermal properties of the phantom materials were in close agreement to well-accepted published results for human tissues. The phantom was able to successfully demonstrate satisfactory operation of the tested heating equipment. The MRI-measured thermal distributions matched the expected patterns for various magnitude/phase settings of the applicator, allowing the phantom to be used as a quality assurance tool. Importantly, the material formulations for the various tissue types may be used to construct customized phantoms that are tailored for different anatomical sites.     

Forearm composition and muscle function in trained and untrained limbs

The influence of a period of training, which lasts for several years, on the proportions of muscle, fat and bone present in the human forearm has been investigated by comparing trained and untrained limbs of nine experienced male tennis players. Ten healthy but untrained males of similar age served as a control group. Computed tomography (CT) scans of the forearm were made at intervals along its length to identify fat, muscle and bone and to calculate the volumes occupied by each of these components. Total forearm volume was greater in the dominant limb compared with the contralateral side in both trained (by 135 +/- 59 cm3, mean +/- SD, P less than 0.001) and untrained subjects (by 41 +/- 45 cm3, P less than 0.02). Forearm muscle volume was also greater in dominant limbs of trained (by 117 +/- 52 cm3, P less than 0.001) and untrained by 35 +/- 41 cm3, P less than 0.025) subjects. Muscle accounted for 75.4 +/- 2.7% of the total volume in the dominant arm of trained subjects compared with 71.4 +/- 4.2% in the control group (P less than 0.05). There was a greater proportion of muscle (P less than 0.05) and a smaller proportion of fat (P less than 0.001) in the trained limb compared with the contralateral limb of the same subjects. No differences in proportions of fat, muscle and bone were observed in dominant and non-dominant limbs of the control subjects. Trained subjects were able to exert a greater isometric force with the dominant limb (549 +/- 76N) than with the non-dominant limb (496 +/- 48N; P less than 0.005). There was no difference in grip strength between the arms of the untrained group (dominant: 516 +/- 107N; non-dominant: 491 +/- 91N). The ratio of strength to muscle volume was, however, the same in dominant and non-dominant arms of both groups of subjects.     

Present and future status of noninvasive selective deep heating using RF in hyperthermia

To achieve hyperthermia using electromagnetic energy, RF of under 100 MHz is basically suitable for the external heating of the deep portions of the body. For applicators using such RF, the following types are considered: capacitive, inductive, radiative and hybrid. With radiative applicators, the intensity of the EM waves radiated from the applicator decreases with propagation into the material to be heated, but the phased annular array of radiative applicators potentially increases the intensity of the EM energy in the deep portion owing to the interference of the waves. Using this method, the focusing of EM energy depends on the dielectric properties of the material to be heated. With respect to RF heating at a lower frequency than the RF used for the annular phased array, some devices have been said to concentrate EM energy in the deep portions, where the characteristics of ‘wave’ are not utilised. To this end, some methods using capacitive electrodes, an inductive coil, or a combination of both, are being designed. The results of using such methods have shown that it is possible to supply sufficient EM energy to the muscle layers deep in the material to be heated, without heating the fat layers excessively.